关注
(5)
in shell command, `true` will always have a 0 error code and `false` will always have a 1 error code.
(6)
`false && echo "Oops fail"`, the second part won't be executed.
Using a semicolon `;` in the middle is a way to concatenate 2 commands.
(7)
to use the output of a command:
`$(command)`
example: `echo "we are in $(pwd)"`
(8)
$0 the name of the script
$# the number of arguments
$$ the process ID of the script
$@ all the arguments
